The sleeve notes from Steeleye Span's Below the Salt album certainly suggest the woman is a prostitute, but I'm not sure the words of the song suggest this.

I first saw her through the swirling mists that rose from the Thames, her body illuminated by the gas-lamp beneath which she stood. Her imitation jewellery reflected the hissing flame and I could just discern the long slit in her skirt and the badly applied rouge on her cheeks. As I neared her she turned towards me in a practised manner. “I've lost my spotted cow,” she said in a voice coarsened by the inclement weather but still retaining the charm of a country accent. I looked at her, suddenly moved. “What brought you to this sorry state?” I asked.